A number of catalysts for olefin polymerization and polymerization processes have been developed so far. However, in order to obtain more sufficient commercial benefits out of such developed catalysts, there have been still great demands for further development on the activity and production yield of a catalyst itself to raise the whole productivity, or on properties of a polymer produced by those developed catalysts to improve the product quality.
There have been reported so far many titanium-based catalysts for olefin polymerization containing magnesium and preparation processes thereof, and also a number of catalyst preparation methods are known in this art, wherein a magnesium compound solution is used in order to control the shape or size, etc. of a catalyst. Methods for obtaining a magnesium compound solution by reacting a magnesium compound with an electron donor such as alcohol, amine, ether, ester, carboxylic acid and the like, in the presence of a hydrocarbon solvent, are commonly known. Among those methods, methods using alcohol are disclosed in U.S. Pat. Nos. 4,330,649 and 5,106,807, and Japanese Patent Laid-Open Sho-58-83006. Further, various methods for preparing a magnesium solution are found in U.S. Pat. Nos. 4,315,874, 4,399,054 and 4,071,674. Particularly, tetrahydrofuran, which is a cyclic ether, has been variously used, for example, to a magnesium chloride compound in U.S. Pat. No. 4,482,687, as an additive for a cocatalyst in U.S. Pat. No. 4,158,642, as a solvent in U.S. Pat. No. 4,477,639 and the like.
Further, U.S. Pat. Nos. 4,347,158, 4,422,957, 4,425,257, 4,618,661 and 4,680,381 disclose a method for preparing a catalyst by adding a Lewis acid compound such as aluminum chloride to a magnesium chloride support and then grinding the mixture.
However, according to those foregoing conventional arts, catalyst properties are not satisfying enough, regarding its morphological properties such as catalyst shape, size and size distribution, and further complement or improvement in stereoregularity of the obtained polymers is also required.
Therefore, to improve the commercial value of such catalyst for olefin polymerization, still required is a preparation method for a catalyst with high polymerization activity and controlled shape and size being capable of providing a polymer with high stereoregularity so as to improve both productivity and product quality.